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These genes are what is inherited. They are extremely useful because
These genes are the “inheritance organisms do not express all of
factors” Mendel discussed. their genes—mostly the dominant
ones. We use the word “genotype”
DNA is simply two strands of
to describe the genetic composition
genes. That is to say, the way
of a cell. Is the cell a TT? Is it a Tt?
traits are inherited as genes. To be
Is it a tt? To talk about which
exact, two copies of each gene in
genes an organism has we use the
inherited. Which version of the
word “genotype”.
gene is expressed (shows in the
offspring) depends on dominance Phenotype, on the other hand, is
as well as other factors. just used to describe the
appearance of the organism. Is it
So, to answer the question “what
round? Wrinkled? Tall? Short? The
are the ‘inheritance factors’
phenotype is the physical trait
discussed by Mendel?”: genes.
expressed.
Different versions of the
Exceptions to Mendel’s
same gene: Alleles
Laws
In every cell there is DNA which is
Incomplete dominance and
composed of two copies of every
codominance
gene. That means, each gene has
a corresponding copy. For Mendel’s laws do not explain when
example, if there’s a tall pea plant traits are averaged. When both a
that means there’s a T gene as well dominant and a recessive trait are
as either another T or a t. These present in the DNA (a
corresponding copies are called heterozygous genotype), but an
alleles. The alleles can either be average of the two traits is
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the same or different . expressed. For example, when a
red Snapdragon Flower is crossed
Genotype and Phenotype with a white Snapdragon Flower,
Genotype and phenotype are the and the F1 offspring are… Pink!
words we use to describe what There is no explanation for that in
genes an organism has, and which Mendel’s laws. According to his
traits are expressed, respectively. laws, the dominant must be
expressed.
This exception is called
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If they are the same they are called “homozygous” incomplete dominance. The
and if they are different they are called
“heterozygous”.
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